1. Field of the Invention
The present invention relates to a linear motion rolling guide unit that linearly guides a movable element to be moved in a linear motion mechanism such as a machine tool or industrial robot.
2. Description of the Prior Art
An example of this type of linear motion rolling guide unit of the prior art is shown in FIGS. 1 and 2. Furthermore, this linear motion rolling guide unit is disclosed in, for example, Japanese Utility Model Laid-Open No. 2-12554.
As shown in the drawings, said linear motion rolling guide unit has track rail 1, formed to have a roughly U-shaped cross-section opening upwards perpendicular to the direction of its elongation, and a slider in the form of sliding unit 3, arranged to be contained within said track rail 1 having rolling element circulating path (to be later described in detail), and able to move freely relative to said track rail 1.
Two track grooves la each, in the form of tracks having a semicircular cross-section, are formed along the lengthwise direction in the right and left inside portions of track rail 1. As shown in FIG. 2, four of said rolling element circulating paths are provided to correspond to each of these track grooves 1a. Each rolling element circulating path is composed of load bearing track groove 4a and return path 4b, each formed mutually in parallel in both the left and right sides of sliding unit 3, and roughly U-shaped direction changing paths (not shown) formed in the vicinity of both the front and back ends of sliding unit 3 which connect each loading bearing track groove 4a and return path 4b at both of their ends. Furthermore, said load bearing track groove 4a opposes track groove 1aof track rail 1.
A plurality of rolling elements in the form of balls 5 are arranged and housed within said rolling element circulating path that bear the load between track rail 1 and sliding unit 3 by circulating while rolling over track groove 1a accompanying movement of sliding unit 3.
The linear motion rolling guide unit having the constitution described above is, for example, arranged on a flat bed 7 in the form of a frame equipped on a machine tool (the entirety of which is not shown). Track rail 1 is fastened to said bed 7 by a plurality of bolts (with hexagon sockets, not shown). Consequently, track rail 1 has flat mounting surface 1b (shown in FIG. 2) for its bottom portion for mounting to bed 7.
Furthermore, as shown in FIG. 2, a plurality of countersunk portions 1c, having a diameter larger than the head portions of the above-mentioned bolts, and insertion holes 1d, having a diameter slightly larger than the threaded portions of said bolts, are concentrically formed in the bottom portion of track rail 1 and in rows in the lengthwise direction of said track rail 1. Said bolts are screwed into bed 7 by being inserted into said countersunk portions 1c and insertion holes 1d so that they are completed embedded. In addition, a plurality of threaded holes 3a are formed in the upper surface of sliding unit 3. Thus, a table supporting a workpiece and so forth (not shown) is fastened to said sliding unit 3 by bolts (with hexagon sockets, not shown) screwed into these threaded holes 3a.
A drive device, which drives the linear motion rolling guide unit 3 described above, is provided, and said drive device is composed as described below.
Namely, said drive device is composed of a ball screw, containing threaded shaft 9, a large number of balls 10, and a nut (not shown), and a torque application device (not shown), such as a motor, that applies torque to said threaded shaft 9 to rotate it. Furthermore, said nut is contained within sliding unit 3, and as is commonly known, together with balls 10 being juxtaposed between thread grooves formed in threaded shaft 9 and said nut, said balls 10 circulate accompanying rotation of threaded shaft 9 while being guided by the circulating path formed in sliding unit 3.
In the linear motion rolling guide unit described above, when threaded shaft 9 is rotated by an external motor, thrust is applied to the nut (not shown) screwed on via said threaded shaft 9 and balls 10 resulting in movement of sliding unit 3. Furthermore, the point of action 0 of this thrust is the axial center of threaded shaft 9.
In the linear motion rolling guide unit of the prior art described above, both arms of track rail 1, formed to have a roughly U-shaped cross-section, have the shortcoming of having low rigidity, being easily deformed in the manner of spreading to the outside due to the load applied to sliding unit 3.
In addition, since the height of the unit is large, the height from bed 7 of a table (not shown) attached on sliding unit 3 also becomes large, thus resulting in the shortcoming of contributing to an excessively large size of the machine tool and so forth in which it is incorporated.